Certain relatively large, complex gas turbine engine components, such as large turbine buckets for land based gas turbine engines, are difficult to manufacture with a directionally solidified (DS) grain structure, such as a columnar or single crystal (SC) grain structure, using well known DS casting techniques. The difficulty results from limitations associated with the investment shell mold strength and with control of melt heat transfer governing unidirectional solidification. The lack and/or loss of mold strength (e.g. mold slumping) during the casting process can result in dimensionally unacceptable cast components.
Moreover, the latest advanced single crystal superalloys include minor alloy additions of yttrium which reacts with the refractory materials commonly used in fabrication of the investment shell mold. Melt/mold reactions can be detrimental to casting chemistry and cleanliness.
It is an object of the present invention to provide an improved directional solidification casting method for making cast components that reduces mechanical stress on the mold and reduces melt/mold reaction effects by reducing contact time between the melt and the mold especially for highly reactive advanced DS and SC alloys.